Rare Earth Derivatives

Uranium(IV) chalcogenolate compounds have been synthesizing with several stoichiometries as the homoleptic [U(SR)4] (R = Et, Pr, Ph) obtained by reaction of [U(BH4)4] or [U(NEt2)4] with thiols or by oxidation of uranium with the disulfide,571 or those bearing cyclopentadienyl rings as [UCp3(ER)] 

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The metallophthalocyanines which have found application as elecfiochromes are mainly the rare earth derivatives, especially lutetium, and second row fiansition metals such as zirconium and molybdenum. Synthesis of these molecules follows the fiaditional routes, e.g. condensation of 1,2-dicyanobenzene with a metal acetate in a high boiling solvent (see Chapter 2). These compounds have structures in which the rare earth element is sandwiched between two phthalocyanine rings, e.g. zirconium bisphthalocyanine (1.92 M = Zr) and lutetium bisphthalocyanine (192 M = Lu), the latter protonated on one of the meso N atoms to balance the charge. 

Cost and abundance are important properties to be considered for any commercial application. Table I lists recent cost and abundance data of individual rare earths derived from major ores. The expensive oxides are the least abundant. Of the catalytically interesting rare earths forming non-stoichiometric oxides, cerium is by far the most abundant and least expensive. 

The Yb(cp)3 complex is both unstable and a strong two photon absorber. Similar absorption has been observed in polydiacetylene (6) and lead glasses (7) at 1064 nm. This may limit usefulness of these materials unless there is a difference in the dispersion of n2 and 0 out to 1300-1550 nm. However other rare earth derivatives are being examined to see if lower values of j3 can be obtained whilst enhancing n2... 

TABLE 9 P-NMR data for rare-earth derivatives [R c P5W30O110]12 > ca ... 

To date, the only rare-earth derivatives of anion 4 are the network solids R4(H20)28[K c P8W48Oi84(H4W4Oi2)2R2(H2O)i0]13-, R = La, Ce, Pr, Nd, that contain both internal and linking rare-earth cations. Additional polytungstate groups are also incorporated within the large central cavity, Figure 31 (Zimmer-mann et al., 2007). 

The superconducting behavior in oxygen defect perovskite oxides is found to depend on the amount and order of oxygen in the structure. In the case of YjBa C y, the highest and sharpest transitions are related to ordering of one-dimensional Cu-O ribbons in the structure which are in turn coupled to a network of adjacent 2-dimensional Cu-O sheets. The isostructural rare earth derivatives of YjBa-jC C y are found to display similar behavior. 

Catalyst synthesis and pretreatment As the history of a catalyst sample is of prime importance for its subsequent activity in catalytic reactions, this subsection is devoted to a brief description of common methods of catalyst preparation and pretreatment. The preparation and pretreatment procedure determines the surface area accessible in the catalytic reaction, the distribution of active surface sites and also the chemical nature of the surface actually involved in the catalytic process. It has to be noted, however, that the detailed microscopic characterization of rare earth derived... 

All known anionic homoleptic rare earth derivatives are shown in table 27 some NMR data in table 28. 

It is interesting to note that, besides the numerous studies concerning transition metal HCF, research has also recently been addressed, specifically to rare-earth derivatives [63-66]. 

RarG Earth Metals. A large variety of rare earth derivatives have been used to initiate ROP of lactones and lactides (46). Their usually high reactivity must be emphasized, as exemplified by the polymerization of a low-strained lactone, )-pentadecalactone, by Y(0-j-C3H7)3 (47) Similarly, /3-BL is polymerized by Y(0CH2CH20Me) at room temperature (48), in contrast to the long reaction time and high temperature required when aluminum-based initiators are used. 

In the last two decades, the rare earth compounds have importantly contributed to the development of polymerization catalysis [6]. Rare earth derivatives are very versatile catalysts that are able to polymerize with high efficiency a large variety of monomers, from olefinic ones to acrylates, and cyclic polar molecules. Controlled polymerization leading to stereoregular polymers and living processes with polymers yielding well-defined macromolecular characteristics giving rise to the preparation of sequenced copolymers are now quite commonly reachable. 

We describe in this chapter our recent results, showing the possibilities offered by controlling transfer reactions in polymerization catalysis involving rare earth derivatives as precatalysts. Borohydrido compounds, which can be used in different catalytic combinations, are emphasized in this frame. We limit our scope to olefinic, nonpolar monomers, which... 

When combined with large excesses of dialkyl magnesium, borohydride rare earth derivatives display a very versatile character, as they afford the chain transfer polymerization of various monomers. By comparison with the stoichiometric addition of MgR2 to borohydride precatalysts, significant changes are noticed. 

Considering the catalytic potential demonstrated by transition metal complexes of porphyrins and phthalocyanines, it seems safe to predict a similarly rich and varied chemistry to be discovered for rare earth derivatives, including aspects pertinent to both catalysis and organic synthesis. 

Pretreatments have involved the immersion of the alloy substrates in a suitable solution, generally at temperatures above ambient, containing rare earth ions to form a mixed oxide-hydroxide containing rare earth derivatives (Li et al, 2010a,b). In such studies, the alloy was anodized in a traditional sulphurie add bath after pretreatment. Li et al (2010a,b) used pretreatment solutions eontaining 75-95 g r of cerium or neodymium nitrates and Imol L of niekel nitrates at... 

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